Conventional methods of making fiber-reinforced composites include bringing together a plurality of fibers with a resin composition and shaping the amalgam of fibers and resin composition into the final composite article. The fibers may include glass fibers that are organized into a woven pattern or randomly assembled into a nonwoven collection or mat. The resin composition applied to the fibers may be a powder, a suspension in a liquid medium, or a melt of thermoplastic polymer.
There can be many challenges applying the resin composition to plurality of fibers to make a homogeneous mixture of the fibers and resin composition in the amalgam. For example, when the resin composition is a powder, there is significant difficulty distributing the particles of the powdered composition beyond the surface of the fibers into the bulk. This can be especially challenging for woven fibers that are difficult or impossible to mechanically mix with the particles. Reducing the particle size to allow them to fit through the interstitial spaces between the fibers may help distribute them beyond the service layer, but milling the particles to very small sizes often requires complex and expensive processing. Moreover, fine-grained particles of organic materials mixed in air can create an explosion hazard, and should be applied to the fibers under an inert (i.e., reduced oxygen) atmosphere.
There are also challenges applying liquid resin compositions to fibers. If the liquid resin composition is a melt of thermoplastic polymer, it often has a viscosity significantly higher than water. A high viscosity melt makes the resin material difficult to impregnate into the bulk of the fibers. Increasing the temperature of the melt to reduce its viscosity can cause unwanted reactions or decomposition in the resin material, making this viscosity-reduction technique of limited value. Another technique increases the pressure on the amalgam using a double belt press in order to drive the high-viscosity melt into the fibers. However, this technique is prone to damaging and distorting the fibers, especially fibers that have been fashioned into a woven fabric. In some instances, the resin material can be mixed or dissolved in a solvent to reduce its viscosity and make it easier to wet the fibers. However, many thermoplastic resin materials are not easily dissolved, and additional time and steps may be required to separate (e.g., evaporate) the solvent from the fiber and resin amalgam. Similar problems can occur for resin compositions made of a suspension of particles in a liquid carrier medium such as water. In addition to the challenges getting the particles to quickly and evenly disperse throughout the fibers, additional steps are often needed to remove the solvent from the amalgam.
These and other problems are addressed by the present application, which includes the making and use of prepregs that have a resin material dispersed in a plurality of fibers. The prepregs may be used in fiber-containing composite articles, and reduce or eliminate the number of time-consuming process steps needed to combine resin compositions with the fibers.